This undated photo made available by the Florida Department of Corrections shows inmate Freddie Lee Hall. / AP

by Richard Wolf, USA TODAY

by Richard Wolf, USA TODAY

WASHINGTON â?? A majority of Supreme Court justices appeared to agree Monday that states cannot declare prisoners mentally disabled and eligible for execution without applying a margin of error to IQ tests.

Five justices sharply questioned Florida's strict standard, under which inmates on death row who score above 70 cannot avoid the death penalty. The high court ruled in 2002 that people with "mental retardation" can't be executed.

"Your rule prevents us from getting a better understanding of whether that IQ score is accurate or not," said Justice Anthony Kennedy, who is likely to be the swing vote in the case.

At issue is whether states such as Florida can apply a rigid test score cutoff without including the "standard error of measurement" relied on by the tests' designers and endorsed by two key clinical groups.

The court's decision, expected by June, will mark the first time it has returned to its landmark 2002 decision in Atkins v. Virginia that said executing people with intellectual disabilities violates their 8th Amendment rights against cruel and unusual punishment.

The key dispute ever since that case was decided has been who gets to define mental retardation, now more commonly referred to as intellectual disability -- states or medical professionals. The high court set a three-prong test that includes intellectual functioning, adaptive behavior and age of onset. But in Florida's case, the latter two prongs are not considered if the IQ score is above 70.

In the case of Freddie Lee Hall, 68, who killed a 21-year-old pregnant woman in 1978 and later killed a deputy sheriff , his lawyers claim he qualifies as mentally retarded. Florida for decades has been trying to execute him.

No one in Hall's precise situation has been executed in the 12 years since the high court prohibited the death penalty for people with intellectual disabilities. Only four other death row residents in Florida and Alabama face similar predicaments.

But the court's ruling could have broad repercussions in the future by spelling out exactly what the justices meant in 2002 when - at least according to Florida and its allies - they prohibited executing the mentally retarded without defining who is and who isn't.

Thirty-two states permit the death penalty. The number of executions peaked at 98 in 1999 but dropped to 39 by last year, according to the Death Penalty Information Center. From 1984 to 2001, 44 people with mental retardation were executed.

Since the Supreme Court's Atkins ruling, several hundred claims of mental retardation have been filed by prisoners on death row, representing about 7% of all cases, according to John Blume, a Cornell University law professor. Slightly more than 100 sentences have been reduced as a result, a 28% success rate.

Several justices appeared to side with Florida, arguing that states deserve some discretion and that clinical groups allow standards to fluctuate.

"This (American Psychiatric Association) is the same organization that once said that homosexuality was a mental disability and now says it's perfectly normal," Justice Antonin Scalia said. "They change their minds."

Justice Samuel Alito noted that the margin of error would permit a prisoner to have an IQ as high as 75, at which point the likelihood he is mentally retarded would be only about 1 in 40.

The court's liberal justices denounced Florida's "bright line" cutoff -- shared by Alabama, Virginia and Kentucky, while several other states using similar criteria -- and defended using the margin of error as a safety valve against executing someone with an intellectual disability.